1. Field of the Invention
The present invention relates to an automated device for maintaining wooden elements on a pressing table for assembling them.
The device is adapted for manufacturing different types of assemblies, such as frame elements, and particularly prefabricated trusses of restricted dimensions known as "gable trusses," and widely used in traditional construction for supporting sloping roofs.
2. Description of Background and Relevant Information
The gable trusses are made by the triangular assembly, on a pressing table, of two principal rafters and a tie beam reinforced by judiciously arranged triangulation parts. The components of the gable trusses are arranged on the pressing table and are generally maintained by mobile abutments sliding in the metal plate grooves of the table and blocked by screws. "Connectors," constituted of metal plates with claws, are then embedded at the junction points by means of mobile jacks borne by a gantry sliding longitudinally above the table.
Most often, the adjustment and setting of the gable trusses, as well as the control of the pressing by the jacks, is done manually. The logs are positioned on the table and maintained by abutments that are positioned manually. The connectors are then pre-embedded by means of a hammer, then the operator positions the jacks above the connectors and activates a lever that allows pressing by the descent of the jacks. The drawback is that, since the adjustment operations are manual, the time required is substantial, causing high labor costs, and the equipment used (mobile abutments, rails) is quickly damaged.
French patent No. 2 693 148, filed by Mr. DEBANNE and Mr. PORTALIER, discloses a device allowing the automatic positioning of the maintaining abutments in the metal plate grooves of the table due to a motoring unit operated by a computer assembly which also controls the movements of the mobile gantry and the pressing jacks.
This equipment has the drawback of requiring a table of a predetermined type, equipped with grooves machined into the plate, which raises its manufacturing costs. Furthermore, the longitudinal displacement of an abutment must be done in three steps, first of all, go to the end of the transverse groove in which it is initially located, then, pass along a longitudinal groove located along the edge of the table, then finally get into a new transverse groove. In cases of maladjustment, the deterioration risks incurred by the abutments, the grooves or the mandrill are substantial.
U.S. Pat. No. 2,707,546, filed on behalf of Mr. Christian DEBANNE, discloses a device allowing the use of any type of table authorizing unlimited displacements of the maintaining elements over the entire surface of the plate and minimizing the consequences of possible malfunctions of the mandrill or of the computer system. This device uses, for maintaining the parts to be assembled, saw logs constituted of cylindrical blocks equipped at the lower portion with tips that get embedded in a wooden plate covering the pressing table, these saw logs being positioned by means of a hollow mobile mandrill equipped on its inner surface with lugs that can slide into the "L"-shaped grooves provided at the periphery of the saw logs and arranged such that the saw logs can be released or made integral with the mandrill by making the latter rotate a fraction of a revolution in one direction or the other.
Not only do the combination of the rotational and translational movements run the risk of decreasing the reliability of the system, but the positioning of the mandrill above a saw log requires great precision which can only be obtained by substantially slowing down the horizontal movements of the mandrill. Above all, the displacement of a series of saw logs to achieve a new configuration requires numerous movements of the motoring unit and the gantry due to the fact that each saw log must be brought to its new location before the system can go back to find the next saw log.